1. Field of the Invention
The present invention relates to an information reproducing/recording apparatus for reproducing/recording information from/to a write-once information recording medium to which information can be recorded while selecting either a land track or a groove track.
2. Description of the Related Art
A blu-ray disc (trademark) is one example of information recording medium having a capacity of 20 GB or more. Blu-ray discs include a reproduction-only BD (Blu-ray Disc)-ROM, a write-once BD-R, and a rewritable BD-RE. In the BD-R, information can be recorded by selecting either a track in a land or a track in a groove provided for a recording layer on a substrate.
An information reproducing/recording apparatus for reproducing/recording information from/to a general optical disc as an information recording medium has an optical pickup. For example, the optical pickup condenses a laser beam emitted from a semiconductor laser device by an objective lens, allows the condensed beam to fall on an optical disc, and receives the beam reflected from the optical disc by a light receiving device, thereby reading information recorded in the optical disc. To accurately read information, automatic control called tracking servo for tracing a track in an optical disc in which information is recorded with a light spot formed on the optical disc by a laser beam emitted from the optical pickup is performed. The tracking servo is performed by driving the optical pickup on the basis of a tracking error signal. The tracking error signal is detected by converting light received by a light receiving part divided plurally in the light receiving device to an electric signal and performing arithmetic process on the electric signal. As the detecting method, 3-beam tracking, push-pull tracking, differential push-pull tracking, differential phase tracking, and the like are practically used.
A tracking error signal has a waveform in which the polarities on the right and left sides are opposite to each other with respect to the center as a reference. The polarity of a tracking error signal is determined by the information reproducing/recording apparatus and changes according to the specifications of the optical pickup, the shape of the track of an optical disc, and the like. For example, in the case of detecting a tracking error signal by the push-pull tracking or differential push-pull tracking and tracing a groove as a groove-shaped track in a BD-R with an optical pickup, the side to which the tracking error signal moves when the light spot is shifted to the inner radius side is set as a plus side, and the side to which the tracking error signal moves when the light spot is shifted to the outer radius side is set as a minus side. In the case of detecting the tracking error signal by the same method and tracing a land as a projected track in a BD-R with the optical pickup, the side to which the tracking error signal moves when the light spot is shifted to the inner radius side is set as a minus side, and the side to which the tracking error signal moves when the light spot is shifted to the outer radius side is set as a plus side. That is, in the push-pull tracking or differential push-pull tracking, the polarity of a tracking error signal in the land and that in the groove in the BD-R are opposite to each other.
The tracking servo is executed in accordance with the polarity of tracking error signal determined as described above. Consequently, in the case where the polarity of a tracking error signal is not correctly set in accordance with the track to be traced, even if the deviation direction of the light spot is determined from the movement direction of the tracking error signal, and the driving of the optical pickup is controlled so as to correct the deviation, the movement and the deviation cannot be corrected, and the tracking servo cannot be performed normally, since all of the movement direction, the deviation direction, and the control direction are opposite and wrong. Therefore, to correctly set the polarity of the tracking error signal before execution of the tracking servo, information indicative of a track (land or groove) in which information is recorded, information of the polarity of a tracking error signal for accurately reading information from the track, and the like is recorded in a PIC (Permanent Information and Control data) area provided at the innermost radius part (about 1 mm) of the recording layer of the BD-R. Although it is easy to read the information from the PIC area after a BD-R is loaded and the tracking servo is performed normally, before start of the tracking servo, the optical pickup cannot be moved with precision, and it is very difficult.
Japanese Unexamined Patent Application Publication (JP-A) No. 2005-243229 discloses the technique of reading a groove wobble signal from an information recording medium and determining that the information recording medium is of a land recording type or a groove recording type from the signal. JP-A No. 2002-358663 discloses the technique of detecting either a land or a groove crossed by a light spot on the basis of an accumulated value for a predetermined period of tracking error signals or the like and determining the kind of the track on which the light spot lands after a track jump. JP-A No. 2002-358673 discloses a learning process of counting the number of times of successes in reproduction when a tracking target position is offset to the plus side or minus side in a retry process at the time of reproduction, performing a statistical process, and shifting the optimum offset of the tracking target position to the plus side or the minus side in accordance with the success rate. Further, JP-A No. 2004-318918 discloses the technique of attempting to obtain address information recorded in an information recording medium at the time of controlling the position of an objective lens in the tracking direction and, when the address information cannot be obtained, inverting the polarity of the tracking error signal. In this document, another technique of loading an objective lens position control program from a recording medium such as another optical disc or a memory card or via a network to a flash memory is disclosed.
Before start of tracking servo on an information recording medium such as a BD-R, the position of a light spot is unknown. Consequently, it is very difficult to read a groove wobble signal from an information recording medium like in JP-A No. 2005-243229 or to read address information from an information recording medium like in JP-A No. 2004-318918. Since the polarity of a tracking error signal is not determined correctly, it is very difficult to determine the kind of a track on which the light spot is positioned like in JP-A No. 2002-358663 or to perform the learning process as in JP-A No. 2002-358673.